Cell Power Input or Hydrodynamics - Which Is More Important in Flotation?

(2011)

Sami Grönstrand

Alejandro Yañez

Gijsbert Wierink

Juha Tiitinen

Abstract

This paper presents the results of the studies carried out at Chuquicamata Concentrator, related to the hydrodynamic set-up of the forced air TankCell® 300. This 300 m3 cell was operating as the first rougher of the line of cells, and its performance was compared to a parallel line with TankCell® 160 machines. In the 300 m3 cell, three different hydrodynamic set-ups were trialed. First, using the new FloatForce® mechanism with the standard rotating speed in the TankCell 300, secondly adding one auxiliary FlowBooster™ impeller in the shaft while maintaining speed, and finally keeping the FloatForce and FlowBooster, but reducing the speed by 10%.
In its initial setup, the single TankCell 300 was measured to be about slightly higher on recovery compared to the two TankCell 160 machines in the parallel bank, while reaching equal grade of copper in concentrate. In this setup, the specific energy consumption, (energy consumed in the cell mechanism and blower) in the TankCell 300 was 0,67 kW per cubic meter. The second and third setup of the TankCell 300 improved the metallurgical results further, and in the third setup also the specific energy consumption was the lowest: 0,58 kW per cubic meter for the TankCell 300. This was unexpected, as recent argumentation points the opposite; that increased power input improves flotation performance. To find the possible reasons for this, metallurgical performance of the single 300 m3 cell in its set-ups is compared to two 160 m3 cells.
Mass balanced and reconciled results from several days’ survey work in each hydrodynamic set-up are presented in terms of global recovery and grade, recovery-by-size and grade-by-size for both copper and molybdenum. Gas dispersion results from all set-ups are also examined. None of the traditional methods indicate the reason for increase in recovery using the FlowBooster, though. As the last test, different residence times were used in the 300 m3 cell with and without the FlowBooster. This test indicates that the kinetic rate of flotation may be higher when using the FlowBooster.
In parallel, research in Computational Fluid Dynamics has progressed in including the bubble pressure for modeling of bubble-particle interactions. Bubble pressure is a result of the ambient flow field surrounding the bubble, and it can be shown that certain range of bubble pressure is beneficial for particle collection. For bubble-particle collision-attachment to occur the energy barrier of attractive Van der Waals forces and repulsive double layer forces must be overcome. Dynamic bubble pressure may be an efficient parameter to assess the kinetic energy budget of bubbles to overcome this energy barrier and make particle capture possible. This “bubble over-pressure” is used to map the collision-attachment regimes in Outotec flotation cells under different conditions. The basic geometry of the Outotec TankCell was modeled using the FloatForce, and with / without the FlowBooster. Results are very interesting, and confirm the full scale plant observations to a degree. The setup with FlowBooster seems to increase the number of bubbles that have their pressure in the optimal range.

Sami Grönstrand, Alejandro Yañez, Gijsbert Wierink and Juha Tiitinen. "Cell Power Input or Hydrodynamics - Which Is More Important in Flotation?" (2011) Available at: http://works.bepress.com/gijsbert_wierink/13/

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